The aim of the current study was to assess the effects of physical exercise on simple reaction time performance. Participants performed a simple reaction time task twice, one time during physical exercise and another time without exercise. Electromyographic signals were recorded from the thumb of the responding hand to fraction reaction time in pre-motor and motor time. The results showed that exercise shortened motor time but failed to affect pre-motor time. This pattern of findings is consistent with previous studies examining the effects of physical exercise on choice reaction time.